Direct Observation of the Reduction of Aryl Halides by a Photoexcited Perylene Diimide Radical Anion

Abstract

The ability of the doublet excited state of perylene diimide anion radical 2(PDI–•)* to reduce aromatic electron acceptors was probed by picosecond time-resolved transient absorption (TA) spectroscopy. Excitation of PDI–• produces visible TA due to 2(PDI–•)* that decays with τ = 160 ps. Aromatic electron acceptors with varying reduction potential quench 2(PDI–•)* and, in some cases, give a new visible region absorption that is attributed to the products of bimolecular photoinduced electron transfer, 2(PDI–•)* + Ar–X → PDI + Ar–X–•. Stern–Volmer quenching of 2(PDI–•)* accomplished with a series of acceptors provides bimolecular quenching rate constants as a function of acceptor reduction potential. Rehm–Weller analysis of the electron transfer quenching data affords the potential for the (*PDI–•/PDI) electrochemical half-reaction as −1.87 V vs SCE.